This program is directed at the Research and Development of a high energy density, electrically rechargeable bipolar Nickel-Metal Hydride (Ni-MH) battery to serve as the internal power supply for a Ventricular Assist Device (VAD). The internal battery pack should store enough energy for 45 minutes of operation in order to give the recipient of such systems maximum portability. The battery pack should be as small and lightweight as possible and have a life of five years. Presently, rechargeable Ni-MH is commercially available in a conventional monopolar spirally-wound cylindrical cell. Implantable prismatic battery packages comprised of cylindrical cells deplete spare body cavities due to intercell voids. The proposed bipolar NI-MH system has the potential of being 50% to 100% smaller than Nickel-Cadmium (Ni-Cd), the only other presently viable battery system by virtue of more efficient use of volume. In addition to excellent performance, the Ni-MH system offers safe operation and employs abundant and environmentally benign materials. Based on the bipolar concept feasibility demonstration activities of Phase I, the Phase II program is directed at the development of this bipolar configuration of the Ni-MH system to maximize volumetric energy density. The goal is to develop a battery that delivers greater than 60 Wh/kg, 150 Wh/l, has a life of 5 years (1826 cycles at one cycle per day) and is compatible with implantable operation.